Spectrometers are used for many purposes. For example, spectrometers are used in the detection of defects in industrial processes, satellite imaging, and laboratory research. However, these instruments have typically been too large and too costly for the consumer market.
Spectrometers detect radiation from a sample and process the resulting signal to obtain and present information about the sample that includes spectral, physical and chemical information about the sample. These instruments generally include some type of spectrally selective element to separate wavelengths of radiation received from the sample, and a first-stage optic, such as a lens, to focus or concentrate the radiation onto an imaging array.
Prior spectrometers and filters, such as linear variable filters, can be used as wavelength separating elements for compact spectrometers. A linear variable filter can be generally configured to have a plurality of transmission profiles, that vary across a length of the filter. Collimated light incident on the linearly variable filter may be spectrally separated by the filter, based on the location at which the incident light hits the filter. A detector optically coupled to the filter can detect the intensity of incident light at different wavelengths. The prior spectrometers and spatially variable filters can be subjected to incident light having a non-uniform intensity distribution across the area of the filter. Such spatial variation of the incident light intensity can produce distortions in the spectral representation of the measured sample.
The prior spatially variable filters for separation of incident light can be less than ideally suited for use with compact spectrometers. For example, prior linear variable filters can introduce distortions into the output spectrum of the incident light. Such distortions may be attributable to, for example, changes in the position and/or orientation of the spectrometer's input window with respect to the sample plane. Therefore, prior spatially variable filters may be less than ideally suited for use with compact spectrometers, which ideally can measure samples at various positions and orientations with respect to the spectrometer's input window.
In light of the above, improved spatially variable filters and compact spectrometers would be beneficial. Ideally, such improved spatially variable filters and compact spectrometers would reduce distortions of the output spectrum due to variations in incident light intensity across the area of the filter.